Long term evolution (“LTE”) of the Third Generation Partnership Project (“3GPP”), also referred to as 3GPP LTE, refers to research and development involving the 3GPP LTE Release 8 and beyond, which is the name generally used to describe an ongoing effort across the industry aimed at identifying technologies and capabilities that can improve systems such as the universal mobile telecommunication system (“UMTS”). The notation “LTE-A” is generally used in the industry to refer to further advancements in LTE. The goals of this broadly based project include improving communication efficiency, lowering costs, improving services, making use of new spectrum opportunities, and achieving better integration with other open standards.
The evolved universal terrestrial radio access network (“E-UTRAN”) in 3GPP includes base stations providing user plane (including packet data convergence protocol/radio link control/media access control/physical (“PDCP/RLC/MAC/PHY”) sublayers) and control plane (including a radio resource control (“RRC”) sublayer) protocol terminations towards wireless communication devices such as cellular telephones. A wireless communication device or terminal is generally known as user equipment (also referred to as “UE”). A base station is an entity of a communication network often referred to as a Node B or an NB. Particularly in the E-UTRAN, an “evolved” base station is referred to as an eNodeB or an eNB. For details about the overall architecture of the E-UTRAN, see 3GPP Technical Specification (“TS”) 36.300 v8.7.0 (2008-12), which is incorporated herein by reference. For details of the communication or radio resource control management, see 3GPP TS 25.331 v.9.1.0 (2009-12) and 3GPP TS 36.331 v.9.1.0 (2009-12), which are incorporated herein by reference.
As wireless communication systems such as cellular telephone, satellite, and microwave communication systems become widely deployed and continue to attract a growing number of users, there is a pressing need to accommodate efficiently a large and variable number of communication devices that transmit an increasing quantity of data within a fixed spectral allocation and limited transmitter power levels. The increased quantity of data is a consequence of wireless communication devices transmitting video information and surfing the Internet, as well as performing ordinary voice communications. Such processes are generally performed while accommodating substantially simultaneous operation of a large number of wireless communication devices.
Significantly enhanced communication services are anticipated to be offered in LTE-A based communication systems by utilization of higher data rates in a communication channel between a user equipment and a base station, with lower latency and reduced cost. Higher data rates can be enabled by carrier aggregation (“CA”), which allows scalable expansion of effective bandwidth delivered to a user equipment through concurrent utilization of communication resources across multiple carriers. The carriers may be of different bandwidths, and may be in the same or different bands. Normal practice in wireless and other communication systems is to deploy a frequency-division duplex (“FDD”) system in a frequency-division duplex spectrum, and deploy a time-division duplex (“TDD”) system in a time-division duplex spectrum. Then carrier aggregation is performed by either FDD-to-FDD carrier aggregation or by TDD-to-TDD carrier aggregation.
It is now a frequent occurrence, however, that a particular cellular operator may have both frequency-division duplex and time-division duplex spectral allocations and in some countries (e.g., Germany), some operators share portions of the time-division duplex spectrum with other operators. In the time-division duplex spectrum, there is a high likelihood that one operator will choose to operate with a time-division duplex system, but that another operator may use the same spectrum to support frequency-division duplex-capable user equipment.
Additionally with respect to the time-division duplex spectrum, separate time-division duplex carriers on adjacent frequencies should be time synchronized so that uplink and downlink transmissions can occur at the same time. If uplink and downlink transmissions on adjacent time-division duplex carriers occur at the same time, however, then the user equipment performing the uplink transmission may cause interference with another user equipment receiving a downlink transmission on the adjacent time-division duplex carrier. An analogous interference may occur at the base station on uplink and downlink transmissions on adjacent time-division duplex carriers occurring at the same time.
The future LTE-A based communication systems will typically be deployed with frequency-division duplex systems and future variants will incorporate time-division duplex systems. Operators are identifying carriers for the time-division duplex systems. Deploying time-division duplex systems, however, is expensive and introduces interference issues in maintaining frequency separation between carriers. Furthermore, as the initial coverage of such time-division duplex system deployment may be limited, good intersystem handover performance to other systems such as a frequency-division duplex system is necessary to maintain service continuity at border areas that are beyond the planned time-division duplex coverage.
Therefore, it is anticipated that some operators may wish to use time-division duplex spectrum for a frequency-division duplex-capable user equipment by utilizing interband carrier aggregation between a frequency-division duplex downlink (“DL”) carrier and a time-division duplex carrier. Additionally, another operator may select a different approach and use time-division duplex spectrum for a time-division duplex system to support time-division duplex-capable user equipment as originally intended. If so, it will become difficult for operators to co-exist because downlink transmissions from an operator using frequency-division duplex carriers for downlink carrier aggregation may interfere with the time-division duplex operator's uplink (“UL”) transmissions. Additionally, a time-division duplex uplink transmission from a user equipment may interfere with a frequency-division duplex downlink reception of a user equipment in a time-division duplex spectrum.
Thus, there is need for an improved method and system that can capitalize on the advantages of carrier aggregation with coexistence between time-division duplex and frequency-division duplex systems that avoids the deficiencies of current communication systems.